The present invention relates primarily to a fluid motor position feedback control system, such as the electrohydraulic or hydromechanical position feedback control system, which includes a fluid motor, a primary variable displacement pump, and a spool-type directional control valve being interposed between the motor and the pump and being modulated by a motor position feedback signal. More generally, this invention relates to the respective fluid motor output feedback control systems and to the respective fluid motor open-loop control systems. In a way of possible applications, this invention relates, in particular, to the hydraulic presses and the motor vehicles. The larger picture of the Energy-Regenerating Adaptive Fluid Control Technology is presented by my several copending US applications including this application and identified also by Ser. Nos. 08/715,470; 08/716,474; 08/715,434; 08/710,323; 08/710,567; 08/725,056.
The hydraulic fluid motor is usually driving a variable load. In the variable load environments, the exhaust and supply fluid pressure drops across the directional control valve are changed, which destroys the linearity of a static speed characteristic describing the fluid motor speed versus the valve spool displacement. As a result, a system gain and the related qualities, such the dynamic performance and accuracy, are all the functions of the variable load. Moreover, an energy efficiency of the position feedback control is also a function of the variable load.
The more the load rate and fluctuations, and the higher the performance requirements, the more obvious are the limitations of the conventional fluid motor position feedback control systems. In fact, the heavy loaded hydraulic motor is especially difficult to deal with when several critical performance factors, such as the high speed, accuracy, and energy efficiency, as well as quiet operation, must be combined. A hydraulic press is an impressive example of the heavy loaded hydraulic motor-mechanism. The load conditions are changed substantially within each press circle, including approaching the work, compressing the fluid, the working stroke, decompressing the fluid, and the return stroke. A more comprehensive study of the conventional fluid motor position feedback control systems can be found in numerous prior art patents and publicationsxe2x80x94see, for example:
a) Johnson, J. E., xe2x80x9cElectrohydraulic Servo Systemsxe2x80x9d, Second Edition. Cleveland, Ohio: Penton /IPC, 1977.
b) Merritt, H. E., xe2x80x9cHydraulic Control Systemsxe2x80x9d. New Yorkxe2x80x94Londonxe2x80x94Sydney: John Wiley and Sons, Inc., 1967.
c) Lisniansky, R. M., xe2x80x9cAvtomatika e Rugulirovanie Gidravlicheskikh Pressov.xe2x80x9d Moscow: Machinostroenie, 1975 (this book had been published in Russian only).
The underlying structural weakness of the conventional fluid motor position feedback control systems can be best characterized by saying that these systems are not adaptive to the changing load environments. The problem of load adaptability of the conventional electrohydraulic and hydromechanical position feedback control systems can be more specifically identified by analyzing two typical hydraulic schematics.
The first typical hydraulic schematic includes a three-way directional control valve in combination with two counteractive (expansible) chambers. The first of these chambers is controlled by said three-way valve which is also connected to the pressure and tank lines of the fluid power means. The second chamber is under a relatively constant pressure provided by said pressure line. In this case, it is not possible to automatically maintain a supply fluid pressure drop across the three-way valve without a xe2x80x9cschematic operation interferencexe2x80x9d with the position feedback control system. Indeed, maintaining the supply fluid pressure drop can be achieved only by changing the pressure line pressure, which is also applied to the second chamber and, therefore, must be kept approximately constant.
The second typical schematic includes a four-way directional control valve in combination with two counteractive chambers. Both of these chambers are controlled by the four-way valve which is also connected to the pressure and tank lines of the fluid power means. In this schematic, it is not possible to automatically maintain an exhaust fluid pressure drop across the four-way valve without encountering the complications which can also be viewed as a schematic operation interference with the position feedback control system. Indeed, a chamber""s pressure signal which is needed for maintaining the exhaust fluid pressure drop, must be switched over from one chamber to the other in exact accordance with a valve spool transition through a neutral spool position, where the chamber lines are switched over, to avoid damaging the spool valve flow characteristics. In addition, a pressure differential between the two chambers at the neutral spool position will affect the pressure drop regulation and may generate the dynamic instability of the position feedback control system.
The problem of load adaptability can be still further identified by emphasizing a possible dynamic operation interference between the position feedback control and the regulation of the exhaust and supply fluid pressure drops.
The problem of load adaptability can be still further identified by emphasizing a possible pressure drop regulation interference between the supply and exhaust line pressure drop feedback pressure systems.
The structural weakness of the conventional fluid motor position feedback control systems can be still further characterized by that these systems are not equipped for regenerating a load related energy, such as a kinetic energy of a load mass or a compressed fluid energy of the fluid motor-cylinder. As a result, this load related energy is normally lost. The problem of load adaptive regeneration of energy is actually correlated with the problem of load adaptability of the fluid motor position feedback control system, as it will be illustrated later.
Speaking in general, the problem of load adaptability and the problem of load adaptive regeneration of energy are two major and interconnected problems which are to be solved consecutively by this invention, in order to create a regenerative adaptive fluid motor position feedback control system, and finally, in order to create a regenerative adaptive fluid motor output feedback control system and a regenerative adaptive fluid motor open-loop control system.
The present invention is primarily aimed to improve the performance qualities and energy efficiency of the fluid motor position feedback control system, such as the electrohydraulic or hydromechanical position feedback control system, operating usually in the variable load environments. The improvement of performance qualities, such as the dynamic performance and accuracy, is the first concern of this invention, while the improvement of energy efficiency is the second but closely related concern.
This principal object is achieved by:
a) shaping and typically linearizing the flow characteristics of the directional control valve by regulating the supply and exhaust fluid pressure drops across this valve;
b) regulating the hydraulic fluid power delivered to the directional control valve, in accordance with, but above, what is required by the fluid motor;
c) preventing a schematic operational interference between the regulation of said pressure drops and the position feedback control;
d) preventing a dynamic operation interference between the regulation of said pressure drops and the position feedback control (as it will be explained later);
e) preventing a pressure drop regulation interference between the supply and exhaust line pressure drop feedback control systems (as it also will be explained later).
The implementation of these interrelated steps and conditions is a way of transition from the conventional fluid motor position feedback control systems to the load adaptive fluid motor position feedback control systems. These load adaptive systems can generally be classified by the amount of controlled and loadable chambers of the fluid motor, by the spool valve design configurations, and by the actual shape of the spool valve flow characteristics.
In a case when only one of two counteractive chambers of the fluid motor is controllable, the fluid motor is usually loaded only in one direction. The controlled chamber is connected to the three-way spool valve which also has a supply power line and an exhaust power line. In this case, the second chamber is under a relatively constant pressure supplied by an independent source of fluid power.
In a case when both chambers are controllable, the fluid motor can be loaded in only one or in both directions. The controlled chambers are connected to a five-way spool valve which also has a common supply power line and two separate exhaust power lines. When the fluid motor is loaded in only one direction, only one of two exhaust lines is also a countepressure line. When the fluid motor is loaded in both directions, both exhaust lines are used as counterpressure lines.
Using the three-way or five-way spool valve with a separate exhaust line for each controllable chamber, makes it possible to prevent a schematic operation interference between the position feedback control and the regulation of pressure drops. In particular, the problem of measuring a chamber""s pressure signal is eliminated. Each counterpressure line is provided with an exhaust line pressure drop regulator, which is modulated by an exhaust line pressure drop feedback signal which is measured between this counterpressure line and the related chamber.
In the process of maintaining the supply fluid pressure drop across the spool valve, a supply fluid flow rate is being monitored continuously by the primary variable displacement pump of the fluid power means. Maintaining the supply fluid pressure drop is also a way of regulating the hydraulic power delivered to the spool type directional control valve.
In the process of maintaining the exhaust fluid pressure drop across the spool valve, all the flow is being released from the counterpressure line through the exhaust line pressure drop regulator to the tank. Counterpressure may be created in the counterpressure line only for a short time while the hydraulic fluid in the preloaded chamber is being decompressed. However, the control over the decompression is critically important for improving the system""s dynamic performance potential.
A family of load adaptive fluid position servomechanisms may include the three-, four-, five-, and six-way directional valves. The three-way spool valve is used to provide the individual pressure and counterpressure lines for only one controllable chamber. The six-way spool valve is used to provide the separate supply and exhaust lines for each of two controllable chambers. The five-way spool valve can be derived from the six-way spool valve by connecting together two separate supply lines. The four-way spool valve can be derived from the five-way spool valve by connecting together two separate exhaust lines. The four-way spool valve does create a problem of schematic operation interference between the position feedback control and the regulation of pressure drops, as it is already explained above. However, the principal possibility of using the four-way spool valve in the adaptive position servomechanisms is not excluded.
What is in common for the adaptive fluid position servomechanisms being considered is that the fluid motor is provided with at least one controlled and loadable chamber, and that this chamber is provided with the pressure-compensated spool valve flow characteristics. These pressure-compensated flow characteristics are shaped by the related exhaust line pressure drop feedback control system which includes the exhaust line pressure drop regulator and by the related supply line pressure drop feedback control system which includes the primary variable displacement pump.
The desired (linear or unlinear) shape of the spool valve flow characteristics is actually implemented by programming the supply and exhaust line pressure drop command signals of the supply and exhaust line pressure drop feedback control systems, respectively. Some possible principals of programming these command signals are illustrated below.
(1) The supply and exhaust line pressure drop command signals are set approximately constant for linearizing the pressure-compensated spool valve flow characteristics. The related adaptive hydraulic (electrohydraulic or hydromechanical) position servomechanisms can be referred to as the linear adaptive servomechanisms, or as the filly-compensated adaptive servomechanisms. Still other methods of programming the pressure drop command signals can be specified with respect to the linear adaptive servomechanisms, as it is illustrated below by points 2 to 5.
(2) The supply line pressure drop command signal is being increased slightly as the respective load pressure rate is increased, so that to provide at least some over-compensation along the supply power line.
(3) The supply line pressure drop command signal is being reduced slightly as the respective load pressure rate is increased, so that to provide at least some under-compensation along the supply power line.
(4) The exhaust line pressure drop command signal is being increased slightly as the respective load pressure rate is increased, so that to provide at least some under-compensation along the exhaust power line.
(5) The exhaust line pressure drop command signal is being reduced slightly as the respective load pressure rate is increased, so that to provide at least some over-compensation along the exhaust power line.
It is understood that the choice of flow characteristics does not effect the basic structure and operation of the load adaptive fluid motor control systems. For this reason and without the loss of generality, in the following detailed description, the linear adaptive servomechanisms are basically considered.
It is a further object of this invention to develop a concept of load adaptive regeneration of a load related energy, such as a kinetic energy of a load mass or a compressed fluid energy of the fluid motor-cylinder. This is achieved by replacing the exhaust line pressure drop regulator by a counterpressure varying and energy recapturing means (such as an exhaust line variable displacement motor or an exhaust line constant displacement motor driving an exhaust line variable displacement pump), by replacing the exhaust line pressure drop feedback control system by an energy recapturing pressure drop feedback control system, and finally, by creating a load adaptive energy regenerating system including fluid motor and load means and energy accumulating means.
It is still further object of this invention to develop a concept of load adaptive exchange of energy between the fluid motor and load means and the energy accumulating, means of the load adaptive energy regenerating system. The load adaptive regeneration of the load related energy of the fluid motor and load means can be viewed as a part (or as a larger part) of a complete circle of the load adaptive, exchange of energy between the fluid motor and load means and the energy accumulating means.
It is still further object of this invention to develop a regenerative adaptive fluid motor position feedback control system which is an integrated system combining the load adaptive fluid motor position feedback control system and the load adaptive energy regenerating system.
It is still further object of this invention to develop a regenerative adaptive fluid motor output feedback control system and a regenerative adaptive fluid motor open-loop control system. In general, the regenerative adaptive fluid control makes it possible to combine the load adaptive primary power supply and the load adaptive regeneration of energy for maximizing the over-all energy efficiency and performance potentials of the fluid motor control systems.
It is still further object of this invention to develop the high energy-efficient, load adaptive hydraulic presses utilizing the regenerative adaptive fluid control.
It is still further object of this invention to develop the high energy-efficient, load adaptive motor vehicles utilizing the regenerative adaptive fluid control.
It is still further object of this invention to develop the high energy-efficient, load adaptive City Transit Buses utilizing the regenerative adaptive fluid control.
Further objects, advantages, and futures of this invention will be apparent from the following detailed description when read in conjunction with the drawings.